The pilots departed when the meteorological forecast gave reason to believe that, in order to reach their destination, the helicopters would have to fly in adverse weather conditions, at low altitude, and over an urban area traversed by electrical transmission lines. As it is difficult to read a chart and identify obstacles and reference points when flying at low altitude, the formation led by the company owner had to follow a highway congested with rush-hour traffic. The fact that the formation leader was the company owner may have influenced the decision of the C-FLYO pilot to continue the flight in adverse weather conditions and to contravene the regulations. Company management was responsible for controlling the operation of its aircraft and for ensuring that the pilots abided by existing regulations. However, for undetermined reasons, the lead pilot chose to guide the formation in adverse weather conditions at an altitude that compromised the safety of the aircraft and its occupants, and persons and property on the ground. While in hovering flight above the first set of cables, the C-FLYO pilot was using the lead helicopter as a visual reference to determine his position in relation to the ground. It was difficult to perceive changes in aircraft attitude because he was hovering high above ground, his field of view was reduced, and the visual reference was moving. The pilot appears to have inadvertently caused the helicopter to drift slightly and lose altitude. When the pilot realized that the aircraft was moving toward the wires, he made a sudden avoidance manoeuvre which culminated in the aircraft landing sideways and rolling over.Analysis The pilots departed when the meteorological forecast gave reason to believe that, in order to reach their destination, the helicopters would have to fly in adverse weather conditions, at low altitude, and over an urban area traversed by electrical transmission lines. As it is difficult to read a chart and identify obstacles and reference points when flying at low altitude, the formation led by the company owner had to follow a highway congested with rush-hour traffic. The fact that the formation leader was the company owner may have influenced the decision of the C-FLYO pilot to continue the flight in adverse weather conditions and to contravene the regulations. Company management was responsible for controlling the operation of its aircraft and for ensuring that the pilots abided by existing regulations. However, for undetermined reasons, the lead pilot chose to guide the formation in adverse weather conditions at an altitude that compromised the safety of the aircraft and its occupants, and persons and property on the ground. While in hovering flight above the first set of cables, the C-FLYO pilot was using the lead helicopter as a visual reference to determine his position in relation to the ground. It was difficult to perceive changes in aircraft attitude because he was hovering high above ground, his field of view was reduced, and the visual reference was moving. The pilot appears to have inadvertently caused the helicopter to drift slightly and lose altitude. When the pilot realized that the aircraft was moving toward the wires, he made a sudden avoidance manoeuvre which culminated in the aircraft landing sideways and rolling over. The pilot was certified and qualified for the flight in accordance with existing regulations. The flight was initiated when the meteorological forecast indicated that, to arrive at their destination, the helicopters would have to fly in adverse weather. The formation leader was the owner of the company, chief of operations, and chief pilot. The formation followed a highway at low altitude, over an urban area. The flight was conducted partially at an altitude lower than that prescribed by regulation. The pilot hovered above an electrical transmission line, at a height where it was difficult to perceive changes in aircraft attitude. The pilot lost control of the aircraft after making a sudden manoeuvre to avoid a wire.Findings The pilot was certified and qualified for the flight in accordance with existing regulations. The flight was initiated when the meteorological forecast indicated that, to arrive at their destination, the helicopters would have to fly in adverse weather. The formation leader was the owner of the company, chief of operations, and chief pilot. The formation followed a highway at low altitude, over an urban area. The flight was conducted partially at an altitude lower than that prescribed by regulation. The pilot hovered above an electrical transmission line, at a height where it was difficult to perceive changes in aircraft attitude. The pilot lost control of the aircraft after making a sudden manoeuvre to avoid a wire. While in hovering flight high above the ground, the pilot lost control of the aircraft after executing a manoeuvre to avoid colliding with a wire. Contributing to the accident were the pilot's decision to continue the flight in adverse weather conditions and the pilot's inadequate visual references while he was hovering above the electrical transmission line.Causes and Contributing Factors While in hovering flight high above the ground, the pilot lost control of the aircraft after executing a manoeuvre to avoid colliding with a wire. Contributing to the accident were the pilot's decision to continue the flight in adverse weather conditions and the pilot's inadequate visual references while he was hovering above the electrical transmission line. Transport Canada is developing guidance material for the interpretation of Canadian Aviation Regulations 702 and 703 (Aerial Work and Air Taxi) which will include the suggestion that operators appoint dedicated Operations Managers and Chief Pilots, separate from the corporate or financial arm of the company. Transport Canada will be reviewing the issue of formation flying through the Canadian Aviation Regulation Advisory Council (CARAC) with a view to establishing further regulatory parameters for this activity. Additionally, hazards associated with formation flying will be the focus of a feature article in the Aviation Safety Newsletter Vortex.Safety Action Taken Transport Canada is developing guidance material for the interpretation of Canadian Aviation Regulations 702 and 703 (Aerial Work and Air Taxi) which will include the suggestion that operators appoint dedicated Operations Managers and Chief Pilots, separate from the corporate or financial arm of the company. Transport Canada will be reviewing the issue of formation flying through the Canadian Aviation Regulation Advisory Council (CARAC) with a view to establishing further regulatory parameters for this activity. Additionally, hazards associated with formation flying will be the focus of a feature article in the Aviation Safety Newsletter Vortex.